This invention relates in general to sheet transport apparatus, and more particularly to a mechanism for use with a sheet transport apparatus for turning over a sheet transported along a travel path.
In transporting sheets along a travel path, it is sometimes required that the sheet be turned over so that the leading edge becomes the trailing edge and its surface orientation is reversed. One typical mechanism for accomplishing such sheet turnover includes a three-roller cluster located in association with the sheet travel path; see for example U.S. Pat. No. 3,856,295 (issued Dec. 24, 1974 in the name of Looney). In such mechanism, the transported sheet is directed into the nip between a first roller and the middle roller of a three-roller cluster and is fed therethrough into a curved chamber until the trailing edge clears such nip. The leading edge of the sheet is directed against a resilient stop which causes the sheet to reverse its direction of travel. Due to the curvature of the chamber and the beam strength of the sheet, the sheet traveling in the reverse direction is directed into the nip between the middle roller and the third roller of the cluster. The sheet is thereby transported back into the travel path with the trailing edge becoming the leading edge and its surface orientation being reversed.
While the use of a resilient stop is generally effective in cooperation with a three-roller cluster for turning over a sheet, it is subject to certain limitations. The resilient stop must have its spring characteristics tailored to the characteristics of the sheet being turned over. That is to say, the stop must have sufficient resilience to assure that the sheet will receive enough impetus to return to the appropriate nip of the three-roller cluster, but must not damage the edge of the sheet as it imparts such impetus. If a variety of weights of sheets must be handled, a resilient stop selected to ensure reversal of movement of a heavy weight sheet may damage the engaged edge of a lighter weight sheet; and a resilient stop selected to prevent damage to a light weight sheet may not provide sufficient impetus to a heavier weight sheet. Further, the resilient stop must be located a distance from the three-roller cluster to ensure that the trail edge of the sheet clears the cluster, that the inertia of the sheet imparted by the cluster will be sufficient to enable this sheet to reach the stop, and that the return impetus is sufficient for the sheet to be returned into the appropriate nip of the cluster. Therefore, the resilient stop must be adjustably located so as to accommodate a variety of sheet sizes (measured in the direction of the travel path) or, if not adjustably located, must be utilized with only a narrow range of sheet sizes.